Loud-speaking telephone



June 15 1926. r

G. SEIBT LOUD SPEAKING TELEPHONE Filed. August 1, 1924 Patented June 15,1926.

UNITED STATES 7 1,588,627 PATENT OFFICE.

GEORG SEIBT, OF SCHONEBERG, NEAR BERLIN, GERMANY.

- LOUD-SPEAKING TELEPHONE.

Application filed August 1, 1924 Serial No. 729,558, and in GermanyAugust 4, 1923.

This invention relates'in general to sound reproducers and moreparticularly to improvements in loud speaking telephones and especiallyto telephone receivers comprising a diaphragm of extremely thin andspecifically light sheet metal e. g. aluminium sheet of a thickness-of.03 mms. and shaped in the form of a curved or conical cup. Inconsequence of the extremely small mass of such diaphragms the upperharmonics of the same are weakened much less than the harmonics of flatdiaphragms. Many attempts have been made to eliminate the disturbinginfluence of the natural periodic'oscillations. of such'diaphragms, butwithout success, so

that the sounds corresponding to the natural rate of vibration of thesediaphragms predominate and the timbre of the sounds to be reproduced isblurred. Thus forexample an aluminium diaphragm of the shape illustratedin the drawing of a diameter-of 100 mms..and .03 mms. in thickness andcarrying an iron armature measuring 12 (12XA mms. has a pretty distinctnatural rate of vibration-of 850 per second.

The object of this invention is to improve the faithfulness of the soundreproduction by effectively damping the natural rate of vibration of thediaphragm. This is accomplished by employing similar damping means forthe diaphragm of a loud speaking telephone as are used in granulartelephonic transmitters i. e. devices in which the diaphragm oscillatedby the sound waves exercises a fluctuating pressure in the rhythm of thesound waves on current conducting granules, e. g. carbon granules,placed behind the diaphragm, and thus gives rise to correspondingfluctuations of the electric resistance and consequently to fluctuationsof the electric current flowing through the ranules. In connection ,with

- such telephonic transmitters or microphones it has already beenproposdto arrange elastic' bodies ,such as layers of felt or the likebehind the diaphragm. These elastic bodies serve as elastic containersfor the granules and also as a means for damping the sound oscillationsof the diaphragm.

In accordance with my invention a light sound-damping material such aslight feathers, 'flufi or down is arranged at the rear of the-diaphragmso as to make contact therewith at numerous farts and over he lightconta t m de" by th said m ter al ith nu.-

merous partsof the surface is very effective 1n damping OblQCtlOIltlllQvibrations. If the 'middle of the diaphragm only were to abut upon asound damping"body such wasa cushion of felt or soft rubber,the upperharmonics resulting from oscillations of parts of the diaphragmwouldnotbe completely suppressed. On the other hand the mea-ns I employ resultnot only in the dampbeen used in all the views to indicate correspondingparts.- In said drawing Fig. 1, is-a sectional elevation showing theapparatus,

Fig. 2, is a similar elevation showing-a modification, and

Fig. 3, is a top plan view of Fig. 2.

In the example shownin Fig. 1 the loud speaking telephone comprises adiaphragm a in the form of acup or disk, said diaphragm being made froma sheet of aluminiunrof a thickness of .03 millimeter. The diaphragm isprovided with a flange clamped between the ring I) of a cylindricalcasing 0 and a, ring d. The diaphragm a carries in its centre asmall-iron armature e which is fixed by a small screw f and a smalldished washer 9. Fixed to the base h of the casing by means of screwsiand washers k is the base plate of an u-shaped electromagnet whosecylindrical pole pieces Z,

which are oppositethe iron armature e, are.

surrounded by coils m through which the voice currents flow. I

The chamber 0 confined by the diaphragm On tapping the middle of a dia-I a, the cylindrical wall 0 and the bottom hot I the casing are filledwith light feathers such as fluff or down. The damping action thusexercisedby the damping agent distributed over the entire surface of thediaphragm results in a talking apparatus or sound reproducer whichreproduces the human voice more distinctly and faithfully than hashitherto been ossible. The illustrated device is a so-callef loudspeaker, i. e. a telephone m.

eeiver which is not held to the ear but throws the sound into thesurrounding space so as to make it audible to a large number of persons.

In Figs. 2 and 3 I have shown a modification in which means are providedfor supporting the mass of light material so that it does not bear withits whole weight on the diaphragm, but merely makes contact therewithwithout exerting material pressure thereon. The general construction ofthe telephone is the same as has been described with reference to Fig.1, and the same retcrence characters have been used to indicatecorresponding parts. In the example shown in the tigures the supportingmeans are in the form of a subsidiary diaphragm a? disposed at the rearof the main diaphragm a and at a distance of say 2 millimeters therefromand provided with a plurality of holes distrihuted over the wholesurface of the diaphragm and permitting the feathers or downs to makelight contact with the main diaphragm a. l have found that thereby agood damping is insured and that the light material does not bear. withits whole mass on the main diaphragm when placing the telephonevertleally or with its dlaphragm at the bottom side, as might be thecase when shipping the telephone. This is important because otherwisethe thin diaphragm is subjeet to injury even by the light dampingmatter.

The supporting diaphragm may be made from sheet metal thicker than .03millimeter, say, .1 millimeter.

I claim p In a loud speaking telephone, a diaphragm of thin sheet metal,an eleetromagnet for oscillating the diapl 'agm, a mass of lightmaterial at the rear of the diaphragm, and means to take up the pressureof said material towards the diaphragm and permitting the material tomake contact with the diaphragm and a foraminated plate at the rear ofthe diaphragm and spaced therefrom and permitting said material to makecontact through its holes with the diaphragm.

In testimony whereof I atlix my signature.

DR. GEORC SFJBT.

